The discovery of an endocannabinoid system in the brain consisting of cannabinoid CB1 receptors and endocannabinoids (e.g., anandamide and 2-AG) has generated a great deal of interest in understanding the physiological functions of this system. Based on converging in vivo and in vitro evidence this system has been proposed to play an active role in processes that underlie the degradation of memory over time (i.e., forgetting) as well as the suppression of learned behaviors that are no longer reinforced (i.e., extinction). Under normal circumstances, these processes are further hypothesized to facilitate the encoding of new information. The studies proposed in this application will examine the function of this system by blocking endocannabinoid signaling either permanently (i.e., CB1 (-/-) mice) or acutely through the use of the CB1 receptor antagonist SR 141716. Although these approaches can indirectly implicate the involvement of endocannabinoids, the availability of mice in which fatty acid amide hydrolase (FAAH), the primary enzyme responsible for anandamide metabolism, has been genetically deleted (i.e., FAAH (-/-) mice) along with a selective FAAH inhibitor will enable us to determine whether this endocannabinoid plays a role in memory. Additionally, we will investigate the neural substrates and receptor mechanisms of action that underlie endocannabinoid modulation of memory. We will ascertain whether the levels of anandamide and 2-AG are modified by behavioral procedures that are found to be under endocannabinoid tone. Finally experiments will also be conducted to determine whether the mnemonic effects of the cannabinoids are mediated in the hippocampus, a brain region that not only contains CB1 receptors and endocannabinoids, but also is known to play a role in learning and memory. Collectively, these studies will further our understanding of the physiological function of this system as well as bridge the gap between the in vitro and in vivo actions of the endocannabinoid system.